The major focus of this research group is the study of responses to genotoxic stress in mammalian cells. This has included the cloning and characterization of a variety of DNA-damage-inducible (DDI) genes. Studies have involved mammalian genes such as the gadd genes beta- polymerase. 06-methylguanine DNA methyltransferase. c-fos, metallothionein, and ubiquitin. Understanding the role of DNA-damage responses in determining the cellular sensitivity to cytotoxic agents, such as used in cancer therapy, is a major objective. An important response to genotoxic stress in all cells are delays in cell cycle progression which are induced by DNA damage. Such delays can have a protective effect since mutants lacking growth arrest responses are hypersensitive to certain DNA-damaging agents. These delays are mediated by various genes and probably include the gadd genes which are both DDI and growth-arrest inducible and which were cloned in this laboratory. The major portions of this project focus on: 1) the study of the expression of these genes and characterization of the cDNA and genomic clones for these five genes; 2) the regulation of these genes with particular emphasis on gadd45; 3) the characterization of the gadd proteins with the development of high-affinity antibodies; 4) elucidation the function of these genes using expression vectors; 5) the use of a transgenic mouse models to study the roles of these genes in vivo; 6) the expression of these genes in human tumor cell lines with known sensitivity to various chemotherapy agents, such as the panel of lines from the NCI drug screening program; 7) the role of the tumor suppressor p53 in mediating DNA damage responses. Of particular interest is our recent finding (in collaboration with M. Kastan and B. Vogelstein) that the induction of the human GADD45 gene is mediated by the p53. This is the first demonstration of a cellular gene whose activation is dependent on p53. This may have important implications in cancer therapy considering that approximately two thirds of human tumors lack normal(wt) p53 function.